The cold truth

ºHypothermia a danger no matter the time of year.

Core body temperature in a typical, healthy human person ranges from about 97.5 to about 99.6 degrees Fahrenheit, according to the accepted medical literature on the subject.

As soon as a person enters a body of water that has a temperature below that range, even by a just few degrees, hypothermia begins to set in.

How quickly depends not only on the temperature of the water but also on the outside temperature and, to a lesser extent, the person's body type and what he or she is wearing.

"Anytime water temperature is lower than body temperature, if you're in it long enough you'll get hypothermic," said South Bend Battalion Chief Al "Buddy" Kirsits, a scuba diver with the Swiftwater Response Team of the South Bend Fire Department for more than 20 years.

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Given that both Lake Michigan and the St. Joseph River rarely rise above 80 degrees Fahrenheit, a person entering either body of water almost always faces some risk of hypothermia, even at the height of summer.

To a certain extent, the river poses an even greater risk than the lake. The fast flowing water acts like a breeze, accelerating heat loss in the body.

"Cold water will pull your temperature down 27 times faster than cold air," Kirsits says, "and fast moving water will pull it down up to 200 times faster."

Managing risk

Hypothermia occurs when the body loses heat faster than it can produce it through thermoregulation, the natural process by which the human body maintains its core temperature.

In extreme cases, a person in the grips of hypothermia can lose consciousness and even die.

"Basically blood flow is being diverted from the skin and periphery and into the internal organs to maintain and regulate the body's internal environment," according to Dr. David Amrhein, a primary care physician with Main Street Medical Group in Mishawaka.